Heretofore in the field of measuring devices generally and digital height gauges specifically various types of probe assemblies have been utilized to sense that exact moment or position at which the probe makes contact with the object being measured. One such probe assembly utilizes the commonly known dial indicator; this approach utilizing a totally mechanical probe requiring the visual discernment of the operator's eye to determine when contact is made. Although great accuracy can be achieved with heighth gauges utilizing dial indicator probes, such probes substantially decrease the operative speed of the gauging system since they are totally mechanical in structure and manual in operation.
To increase the operational speed of heighth gauge systems the art has developed certain electronic probe assemblies. These probe assemblies are generally such that when the probe makes contact with a surface an electric signal is created thus indicating to the appropriate circuitry that a measurement should be made. Certain of these electronic probe assemblies utilize pivotal probes which are operatively connected to inductor-type circuitry such that the pivotal movement of the probe caused by contact of the probe with an object will create a signal through the inductor-type circuitry thus signaling that a measurement must be made. Such probe assemblies require that the probe utilized therewith be of a specific length since the signal created is indicative of a pivotal motion. Consequently, varying length probes may not be utilized with the same assembly unless compensation means are provided for with the inductor-type circuit.
Some known electronic probes utilize LVDT's wherein the probe is connected to the movable core thereof while the LVDT housing, containing the coils thereof, is fixedly attached to the probe assembly proper. As is well known to those skilled in the art, the cores of such LVDT's are generally spring biased against a stop pin such that contact of the probe attached to the core changes the positional relationship between the core and the coils thus changing the output signal from the LVDT. Being mechanically biased by means of the spring, such probe assemblies are unidirectional only; that is, the probe may sense only in a downward or upward moving relationship with respect to the object to be sensed but not in both directions. The mechanically biased probe assembly is not electrically zero centered so that bi-directional measurements may be made. For such a probe assembly to be utilized for making measurements in either direction of travel, the probe assembly must be inverted each time that the direction of movement of the assembly is changed.
Further, many known probe assemblies are such that sensing is accomplished at the exact moment that the probe makes contact with the surface to be measured. Such probe assemblies do not automatically take into account the diameter of the probe tip being utilized but leave that factor to the user to take into account when recording his measurements.
Consequently, it is an object of the instant invention to present a bi-directional zero radius auto-fire probe and amplifier wherein the probe moves in a straight line so that it may be of any of numerous lengths.
Yet another object of the invention is to present such a probe assembly wherein a LVDT is utilized to create the measurement signal and wherein the LVDT is electrically zero centered so that bi-directional measurements may be taken.
Still a further object of the invention is to provide a measurement probe assembly wherein compensation for the radius of the probe tip is automatically made.
Yet another object of the invention is to present a measurement probe assembly which is substantially immune to jarring or shaking which, in many known probe assemblies, results in false readings.
Another object of the invention is to present a measurement probe assembly which has selectable degrees of sensitivity and which automatically produces a binary logic signal when the probe tip is displaced a distance equivalent to the radius thereof.
These objects and other objects which will become apparent as the detailed description proceeds are achieved by a bi-directional, zero radius, auto-fire probe and amplifier assembly for utilization with a digital height gauge for creating signals indicating when a measurement should be taken, comprising an LVDT having primary and secondary coils and a core positioned therebetween; a probe having a tip thereon operatively connected to and movable with the coils; first circuit means connected to the LVDT for receiving electrical signals therefrom indicative of the positional relationship between the coils and the core and producing a DC output signal therefrom; and second circuit means connected to and receiving the DC output signal from the first circuit means, the second circuit means creating the signals indicating that a measurement should be taken.